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A survey for seroprevalence of Chagas disease was held in a representative sample of Brazilian individuals up to 5 years of age in all the rural areas of Brazil, with the single exception of Rio de Janeiro State. Blood on filter paper was collected from 104,954 children and screened in a single laboratory with two serological tests: indirect immunofluorescence and enzyme linked immunoassay. All samples with positive or indetermined results, as well as 10% of all the negative samples were submitted to a quality control reference laboratory, which performed both tests a second time, as well as the western blot assay of TESA (Trypomastigote Excreted Secreted Antigen). All children with confirmed final positive result (n = 104, prevalence = 0.1%) had a follow-up visit and were submitted to a second blood collection, this time a whole blood sample. In addition, blood samples from the respective mothers and familiar members were collected. The infection was confirmed in only 32 (0.03%) of those children. From them, 20 (0.025%) had maternal positive results, suggesting congenital transmission; 11 (0.01%) had non-infected mothers, indicating a possible vectorial transmission; and in one whose mother had died the transmission mechanism could not be elucidated. In further 41 visited children the infection was confirmed only in their mothers, suggesting passive transference of maternal antibodies; in other 18, both child and mother were negative; and in 13 cases both were not localized. The 11 children that acquired the infection presumably through the vector were distributed mainly in the Northeast region of Brazil (States of Piauí, Ceará, Rio Grande do Norte, Paraíba and Alagoas), in addition to one case in Amazonas (North region) and another in Parana (South region). Remarkably, 60% of the 20 cases of probably congenital transmission were from a single State, Rio Grande do Sul, with the remaining cases distributed in other states. This is the first report demonstrating regional geographical differences in the vertical transmission of Chagas disease in Brazil, which probably reflects the predominant Trypanosoma cruzi group IId and IIe (now TcV and TcVI) found in this state. Overall, these results show that the regular and systematic control programs against the transmission of Chagas disease, together with socioeconomic changes observed in Brazil in the last decades, interrupted the vectorial transmission in Brazil, resumed in the few cases found in this national survey. Furthermore they reinforce the need for maintenance of control programs for the consolidation of this major advance in public health.

This article aims to correlate the main results of three large national surveys on Chagas disease (entomologic, seroprevalence and electrocardiographic) carried out in Brazil from late 1970's to early 1980's, which served as baseline for definition of the control measures adopted in the country. The proportion of infected people was much higher in areas where Triatoma infestans, the most efficient vector of Chagas disease among the five principal species involved in transmission at that time, was predominant. Similar result was observed in places where Triatoma sordida was dispersed, mainly in the country's central region, which corresponds to its native area. This finding is due to the coincidence observed in the geographic distribution of both vectors, since T. sordida is not considered to play an important role in transmission. In the Northeastern semi-arid, endemic area for Triatoma brasiliensis and Triatoma pseudomaculata, rates of human infection were much lower, although both vectors may have some relevance in the maintenance of the disease. As for areas with Panstrongylus megistus, human infection varied according to the levels of domiciliation. Whenever domiciled, like in the humid northeastern coastal area, its involvement in transmission can be clearly demonstrated. In some parts of Bahia State it represented the exclusive vector of the disease. Based upon the results of the seroprevalence survey an electrocardiographic study was carried out in 11 Brazilian states, which showed marked differences in the presence of cardiac alterations when comparing different areas of the country.

In order to assess the evolution of seropositivity for Chagas' disease in the rural community of Cássia dos Coqueiros, in São Paulo state, we compared two cross-sectional studies performed at that site in 1971-1972 and in 1989-1991. In the first survey the complement fixation test was used to determine seropositivity for the disease. In this study, the total prevalence of Chagas' disease was found to be 16.6%, with values ranging from 2.9 to 61.9% (in the 10-19 and 50-59 year age groups, respectively). In the 1989-1991 study, in which indirect immunofluorescence was used, the total prevalence dropped to 10.1%, with a minimum of 0.4% (in the 10-19 year age group) and a maximum of 44.8% (in persons over 60 years of age). Among subjects born in Cássia dos Coqueiros, the 1989-1991 study showed seropositivity after age 38, with only one exception (a 24-year-old man). The drop in the seropositivity index for Chagas' disease in Cásia dos Coqueiros during the period under study can be partially attributed to socioeconomic factors, such as improved living conditions and the progressive abandonment of rural areas. Thus, our results point to the spraying of households with residual insecticides, which began in 1950, as the pivotal factor in the fight against triatomine bugs and in disease control. These results suggest that transmission may have been interrupted as early as the latter part of 1954 and later consolidated as a result of improved socioeconomic conditions and the elimination of Triatoma infestans from the study area.